Create custom MCE wysiwyg functions. Below example gives user the ability to create custom buttons and text color in wysiwyg.

mce_buttons.php

/**
 * ADD STYLES TO WYSIWYG
 */
// Insert 'styleselect' into the $buttons array
function my_mce_buttons_2( $buttons ) {
    array_unshift( $buttons, 'styleselect' );
    return $buttons;
}
// Use 'mce_buttons' for button row #1, mce_buttons_3' for button row #3
add_filter('mce_buttons_2', 'my_mce_buttons_2');

function my_mce_before_init_insert_formats( $init_array ) {
    $style_formats = array(
		array(
            'title' => 'Button', // Title to show in dropdown
            'inline' => 'a', // Element to add class to
            'classes' => 'wysiwyg-btn' // CSS class to add
        ),
        array(
            'title' => 'Trajan', // Title to show in dropdown
            'inline' => 'span', // Element to add class to
            'classes' => 'cinzel' // CSS class to add
        )
    );
    $init_array['style_formats'] = json_encode( $style_formats );
    return $init_array;
}
add_filter( 'tiny_mce_before_init', 'my_mce_before_init_insert_formats' );


// EDITOR STYLES

function mm4_you_add_editor_styles() {
    add_editor_style( 'custom-editor-style.css' ); // add css to root
}
add_action( 'admin_init', 'mm4_you_add_editor_styles' );